1. Field of the Invention
The present invention relates to a spigot-and-socket joint which is secured against separation or pulling apart under high pressure fluid flow across the joint.
In particular, an elastomeric or rubber ring having toothed metal segments is placed in a conical chamber in the socket end and a compression ring is placed in the same chamber to push the rubber ring with the toothed metal segments in a direction to force the teeth of the toothed segments into contact with the spigot end of a pipe enclosed in the socket of a second pipe. To prevent a fracture of the pipe bell when toothed segments abut against the outer wall of the socket, the socket has a recess and the segments have shoulders which engage the recess to convert a wedge force into an axial force.
2. Description of the Prior Art
A similar joint is illustrated in U.S. Pat. No. 4,805,932, issued Feb. 21, 1989. This patent shows a spigot-and-socket joint which is secured against pulling apart, wherein the spigot end of one pipe is pushed into the socket end of another pipe, with radial play. The joint comprises a sealing ring and a gripping ring in the socket pipe, the gripping ring comprising a plurality of metal gripping segments mutually spaced circumferentially and each having a spherically convex radially outer surface and being interconnected in the circumferential direction by a vulcanized intermediate piece of rubber or the like, and a toothed configuration on the radially inner surface, so that when axial tensile forces arise at the joint, the toothed configurations are pressed radially inwardly against the spigot end by interaction of the spherically convex surfaces with an interior conical surface of the pipe socket which interior surface narrows in the direction of the distal end of the socket. In order to effectively eliminate relative radial movements of the gripping ring when the joined pipes are first subject to interior fluid pressure, an elastomeric holding piece is formed on the gripping ring, which gripping ring is separate from the sealing ring, the holding piece being attached to the distal end face of the socket and supporting the gripping ring.
It has been found that in actual practice the holding piece, referred to as a collar in the patent, causes serious problems. When the spigot end of one pipe is pushed into the socket end of the other pipe, the toothed elements move inwardly of the socket but the rubber web between the elements does not move uniformly and can cause uneven distribution of the toothed elements.
Additionally, at extreme fluid pressures, it has been found that one or more segments can protrude past the distal end face of the socket and with a wedging force fracture the socket.
The patented joint has failed at a pressure lower than desired.
An improvement in the prior art over that described in U.S. Pat. No. 4,805,932 has been developed. The improvement comprises the elimination of the collar or holding piece formed on the gripping ring and the insertion of a compressible elastomeric ring located between the gripping ring and a radial wall in the socket. The compressible ring applies a force to the gripping ring to insure tight contact between the toothed configurations of the gripping ring and the spigot end of one of the pipes.